(1) Field of the Invention
This invention relates to a ply-turning device for use in tire-building.
(2) Description of the Prior Art
In large size tires which are typically a so-called off-the-road tire (OR tire) predominantly used on rough ground under a heavy loading, each of the bead portions is often required to be reinforced with a plurality of bead cores, for example, two or three bead cores arranged adjacent to each other in a direction parallel to the rotational axis of the tire. In any case, a first drum for the formation of a first green case to be used at the initial building stage of such a large size tire protrudes axially and outward in a radial direction at both side edge portions. Therefore, when a surplus portion of a carcass ply is wound around a bead core located inward at each of the protruding side edge portions and turned upward in the radial direction, it is difficult to intimately join the surplus turnup portion to the carcass ply along the protruding side edge portion of the drum.
For this reason, it has hitherto been proposed a method wherein the surplus portion of the carcass ply is wound around the bead core and turned upward by using a toroidal bladder capable of expanding in the radial direction near each side edge portion of the first drum (See, for instance, Japanese Patent Application Publication Nos. 36-434 and 45-27,467). In this method, however, there are some serious drawbacks that the expansion stroke of the bladder along the protruding side edge portion is too long, the expansion resistance conspicuously increases due to the protruding, it is difficult to completely join the end of the surplus portion to the carcass ply at a final stage, and the large diameter of the bladder itself often causing puncture is dangerous in the workability, i.e. in view of the maintenance of safety in the factory.